Two planes came dangerously close to each other midair, but narrowly avoided a crash.Source: Supplied

IT WOULD have been among the worst disasters in aviation history, and authorities are baffled about what went so wrong.

Two Boeing 747 aircraft, carrying a combined 1000 passengers, almost crashed over Scotland after all four pilots accidentally turned the planes onto a collision course, the Daily Mail reports.

The transatlantic planes were preparing to cross the ocean when an air traffic controller on the ground noticed they were converging on each other.

The plane on the left was ordered to go left, and the plane on the right was ordered to go right, to avoid crossing paths.

But the pilots aboard both planes misinterpreted the instructions and did the opposite.

A midair disaster was only avoided at the very last second, when the four pilots physically saw the other planes and took evasive action. One plane climbed in altitude while the other dived.

An investigation has been going since the near-miss occurred, in broad daylight on 23 June 2013. The details of the investigation have only just come to light in a report by the UK Airprox Board, which looks into aviation incidents.

The expert investigators are at a loss to explain it.

"It was apparent that both crews had taken each others' instructions," the report concludes.

But it adds the experts found it hard to determine why this had occurred".

The report said the crews may have been distracted as they received clearances to cross the ocean and settled into their transatlantic routine, and were caught off guard by the alert.

"Expecting only routine information to be transmitted at that time, they may have been perplexed by the avoiding action information and instinctively responded without properly assimilating it," it said.

The board said the danger to the aircraft was increased because they had earlier needlessly been ordered by air traffic control to fly at the same height - 34,000 ft.

It is not known which airline or airlines were involved in the incident. It came a few months before a similar incident in Australia in September, when two Qantas planes came within seconds of colliding in the air.

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